Pedicle screws held by clamps in osteosynthetic assemblies are one type of implant used for treating spinal injuries and deformities. In one common treatment the pedicle screws are driven into the pedicles of vertebrae above and below the injured vertebra or vertebrae. A supporting rod is attached to the pedicle screws, for example, by clamps or by threading it through slots in the pedicle screws. The supporting rod holds the spinal column approximately in its desired alignment, thereby relieving pressure on the injured vertebra or vertebrae and permitting it to heal and regain its natural conformation.
One type of pedicle screw is disclosed in U.S. Pat. No. 4,887,596, filed Mar. 2, 1988, commonly owned herewith.
As noted, clamps may be used to connect rigidly the part of the pedicle screw protruding from the vertebra to a spinal support rod. In most of these known clamps the pedicle screw and the supporting rod are arranged in the same plane allowing no adjustment to anatomical requirements.
In another known type of pedicle screw clamp (according to AT-B 387,710 to Sulzer) the central axis of the pedicle screw and the central axis of the support rod are located in different planes but are still maintained at a fixed, non-adjustable distance, again preventing the surgeon from adapting the clamp to anatomical needs. Furthermore, these known pedicle screw clamps do not permit relative angular adjustment of the pedicle screw and the support rod. Thus, current clamps do not allow sufficient adjustment to the specific alignment required by each patient's needs.